Since laser beam machining is capable of delineating fine patterns of an order of a micron (μm) without requiring a lithography process, it has been attracting a great deal of attention as an approach to manufacturing semiconductor devices. In producing semiconductor devices, various types of layers, such as resist layers, resin layers, insulating layers, metal layers, etc. are formed and laminated on a wafer. Fine machining is needed not only for forming VIA holes, circuit patterns, and interconnections in the laminated layers, but also for grooving wafers for, e.g., the purpose of promoting wafer sawing.
Wafer sawing is performed by a combination of the laser grooving process and mechanical diamond blade dicing to prevent peeling problems, which cannot be addressed by a standard blade dicing process alone. The action of groove definition via the laser grooving process generally results in debris such as silicon debris on the wafer surface and groove sidewalls that contain undesirable crystal imperfections. Accordingly, in the traditional laser grooving process, a step of cleaning grooves scribed by a laser scriber with an etchant comprising a base and peroxide mixture, an acid and peroxide mixture, a NaOH solution, or several other solutions known and used in the art to remove debris from the grooves and the top surface of the wafer is required. However, this etching step must be done carefully to avoid removal of all the top surface oxide. Further, it is difficult to entirely remove the accumulated debris by the standard cleaning methods. It is also known to coat a protective material on the surface of the wafer prior to the laser grooving process to prevent the adherence of the debris. However, additional processes, such as for covering the active areas and the bumps on the wafer with the protective material and for removing the protective material on the wafer, are required.
Excimer lasers have been considered poor choices as exposure radiation sources for machining metals due to the generation of severe recast and debris during the laser interaction. High repetition rate, Q-switched YAG lasers also generate a recast and debris field when machining metals. These YAG lasers may be focused to a small spot and rastered over the area to be cut so that the generation of recast and debris may be somewhat tempered. However, the generation of recast and debris using a YAG laser in this way will still not be eliminated or even suppressed below a sufficient tolerance level.
Hence, because of the defects in the prior arts, there is a need to solve the above problems.